1. Field of the Invention
This invention relates to improvements in a defogging article having a defogging ability and a method of producing the same, and more particularly to the improvements for long maintaining the defogging ability of a defogging coating formed on a substrate such as a glass plate, a mirror, a metal article and a plastic article.
2. Description of the Prior Art
Inorganic glass and the like has been hitherto extensively used as the material of glass articles such as windowpanes, mirrors, and lenses of spectacles (glasses) by virtue of transparency thereof. However, these transparent glass articles unavoidably cause dew condensation when used at a high temperature and humidity place or at a border of places largely different in temperature and humidity, so that the surface of the articles is clouded with condensed dew.
It is a particularly serious problem that the windowpanes, the lenses of spectacles, the mirrors and the like are clouded with condensed dew and tends to easily scratch. Accordingly, improvements to solve the serious problem have been eagerly desired in a variety of fields. In view of this, a variety of proposals have been made to provide a defogging ability and a durability to the articles including a transparent material such as glass.
For example, in order to prevent the surface of a glass plate or the like from being clouded, a proposal has been made in which a hydrophilic coating is formed on the surface of the glass plate or the like. In this regard, it has been known as a simplest way from old times that the glass or the like can be prevented from being clouded by coating a surface active agent on the surface thereof. The proposal is to blend a water-soluble polymer such as polyacrylic acid or polyvinyl alcohol with the surface active agent thereby trying to improve the continuation of a defogging ability, as disclosed in Japanese Patent Provisional Publication No. 52-101680. However, this proposal can provide only a temporary defogging ability and therefore it is impossible to expect a continuous defogging ability.
Japanese Patent Provisional Publication No. 55-154351 discloses a proposal to form a hydrophilic coating having a defogging ability on the surface of a glass plate by physical deposition, chemical deposition or the like. The hydrophilic coating includes phosphate and at least one of molybdenum oxide and tungsten oxide. Additionally, Japanese Patent Provisional Publication No. 54-105120 discloses a proposal to provide a defogging ability to a glass containing P.sub.2 O.sub.5 by contacting liquid or vapor of P.sub.2 O.sub.5 to the glass. Further, Japanese Patent Provisional Publication No. 53-58492 discloses forming a defogging coating which is high in adhesion, by coating on a substrate a composition including sulfonic acid type ampholytic surfactant and inorganic salt or acetate, in the form of a lower-alcoholic solution.
However, difficulties have been encountered in the above discussed proposals, in which the defogging ability cannot be long maintained in any defogging coatings. Additionally, the defogging coatings of the above proposals are lower in weatherability thereby shortening the life of the defogging coating.